1. Field of the Invention
The present invention relates to a shift mechanism and a vehicle or motorcycle equipped therewith. More particularly, the present invention relates to a shift mechanism used in a twin clutch transmission and a vehicle equipped therewith.
2. Description of the Related Art
Heretofore, a transmission has been known that is equipped with a plurality of clutches in order to make possible speedy transmission operations of an automobile (see Unexamined Japanese Patent Publication No. SHO58-124851, for example).
A vehicular multi-speed transmission of Unexamined Japanese Patent Publication No. SHO58-124851 is equipped with an input shaft by which a driving force of an engine is input, a first auxiliary shaft provided rotatably with respect to the input shaft, a second auxiliary shaft provided on the same axis line as the input shaft, a counter shaft provided parallel to the input shaft, an output shaft connected to the counter shaft, a first clutch provided between the input shaft and the first auxiliary shaft, and a second clutch provided between the input shaft and the second auxiliary shaft.
The input shaft that inputs and engine driving force is passed through the inside of the first auxiliary shaft and is connected to the second auxiliary shaft via the second clutch. With this vehicular multi-speed transmission, the first auxiliary shaft rotates through having the torque of the input shaft transferred by connection of the first clutch, and the second auxiliary shaft rotates through having the torque of the input shaft transferred by connection of the second clutch.
Furthermore, on the first auxiliary shaft and the counter shaft, a plurality of gear sets corresponding to odd-numbered gears that transfer power from the first auxiliary shaft to the counter shaft, are provided. On the second auxiliary shaft and the counter shaft, a plurality of gear sets corresponding to even-numbered gears that transfer power from the second auxiliary shaft to the counter shaft, are arranged. Transfer of power via these gear sets corresponding to odd-numbered and even-numbered gears is performed with switching of the first and second dog-clutch gear ratio switching units that are placed on the counter shafts so as to rotate integrally with the counter shafts and be able to slide on splines.
The first and second switching units are operated by actuators and so on according to the switching of connected and disconnected states of the first and second clutches, and switch the gear sets to transfer power to the counter shafts to gear sets corresponding to predetermined transmission gears.
Thus, with a conventional vehicular multi-speed transmission, torque of an input shaft is transferred to counter shafts at varying gear ratios, by alternately connecting and disconnecting the first and second clutches in accordance with the transmission operations of gear switches, without interrupting engine drive transfer. As a result of this structure and arrangement, it is possible to vary the rotation speed of the output shaft and enable transmission in the vehicular multi-speed transmission accordingly.
The first and second gear ratio switching units are generally operated by shift forks of a shift unit that is driven by an actuator, and, for the shift unit, there is, for example, the shift unit disclosed in Unexamined Japanese Patent Publication No. HEI7-139627.
With this shift unit, shift forks that engage with the first and second gear ratio switching units respectively at the front end are provided slidably on two fork axes that are parallel to an input shaft, first auxiliary shaft, second auxiliary shaft, and counter shaft. These shift forks are internally fitted in grooves, in a slidable fashion, provided in the outer periphery of a shift drum. By rotation of this shift drum, the shift forks move on the fork axis, and the first and second gear ratio switching units at the front end move accordingly on the counter shaft in the direction of splines, allowing gear shifting. When the first switching unit is in a neutral position, torque of the first auxiliary shaft is not transferred to the counter shaft. Likewise, when the second switching unit is in a neutral position, torque of the second auxiliary shaft is not transferred to the counter shaft.
Now, with a vehicular multi-speed transmission with a plurality of clutches such as the one disclosed in Unexamined Japanese Patent Publication No. SHO58-124851, every time the gear ratio changes one gear, the first and second gear ratio switching units move to a neutral position alternately.
Consequently, when one of the first and second gear ratio switching units and the gear of one of the first and second auxiliary shafts corresponding to this one of the gear ratio switching units are connected by a dog mechanism, cases might occur where, upon connection, the dog of the gear ratio switching unit and the dog of the gear do not synchronize and mesh. To help support such cases, substantial force is required in order to connect one of the first and second gear ratio switching units from the neutral position to a gear.
However, according to the conventional shift unit disclosed in Unexamined Japanese Patent Publication No. HEI7-139627, it is not possible to apply large torque to a shift cam, and, consequently, there is a threat that poor connection between the first and second gear ratio switching units and the corresponding gears makes smooth gear shifting difficult.